the same model used in the newtown, connecticut, school shooting. tomasz kaczowka and mike chiapperini were killed. spengler killed himself. and late today, human remains were found in spengler's house and suspect they belong to his missing sister. >> microsoft is always the burning question. i'm not sure we'll ever know what was going through his mind. >> reporter: police are investigating whether the death of spengler's mother could help explain the motive for her son's christmas eve shootings. ron mott, nbc news, new york. >>> tonight, billions around the world are gathered with family and friends to celebrate christmas. at the vatican downlotoday, pop benedict called for peace. and today marks the 12th christmas in a row that american troops are serving in afghanistan. more than 66,000 u.s. service members are still there, many of them getting some time to attend church services and celebrate with a proper christmas lunch. >>> back in this country, amid neighborhood celebrations and family gatherings across the country, it's a somber christmas d